1. Field of the Invention
This invention relates to multiplexing techniques for controlling operation and obtaining status, over a single wire bus, of a plurality of electrical devices disposed throughout a motor vehicle and, more particularly, in a preferred embodiment to systems for commanding the operation of a plurality of smart single controllers each of which controls the operation and senses the status of a single electrical device such as a motor, a lamp, a relay, etc. disposed near the single controller.
2. Description of the Prior Art
The present inventor and Frederick O. R. Miesterfeld in U.S. Pat. No. 4,736,367 entitled "Smart Control and Sensor Devices Single Wire Bus Multiplex System", which issued Apr. 5, 1988, taught using a plurality of smart control elements for controlling individual relay drivers that operate individual conventional mechanical relays to switch ON and OFF motors, other relays, lights, etc. and using a plurality of smart sensors to monitor the operation of a plurality of switches; i.e., whether the switches are open or closed. Also, this system provides diagnostic information concerning the smart control elements and smart sensors.
Each smart control element and each smart sensor connects at a separate single point on a single wire bus. A microcomputer and a driver/receiver circuit develops and places on the bus a particular offset square wave pulse train which provides power and control voltage signals to the plurality of smart control elements and smart sensors.
The smart control devices contain circuits that respond to the offset square wave pulse train in a manner causing each smart control element to drive an associated relay driver after a chosen number of polling cycles dictated by address codes formed by various voltage levels of the pulse train. Current signals are sent over the bus back to the driver/receiver circuit indicative of the status of the smart control device.
The smart sensors contain circuits that respond to the square wave pulse train in a manner that causes each smart sensor to send current signals back over the single wire bus to the driver/receiver circuit and then on to the microcomputer during designated repetitive and sequential time slots.
The driver/receiver circuit receives, interprets and converts the current signals from the smart control elements and the smart sensors into voltage signals used by the microcomputer for establishing a history of the status of the bus, the control elements, the sensors and the switches.
The microcomputer supplies continuous and updated information to a display system indicative of the status of each control element and each sensor and its associated switch.
This system requires wave train signals to poll and address the same control element several times before the associated relay driver circuit operates the relay. This polling scheme obviously consumes added time to effect the operation of the end device.